For a couple of reasons: I was pretty sure some laws had been broken, serious laws, and at one point I was threatened and that pissed me off; the reporter I spoke to was the second one to contact me about the issue, so I figured my name was floating around out there related to this issue and it was possible I could end up being written about in a story if I didn’t work with a reporter. For the record, I had communicated my concerns to relevant law enforcement and all relevant files before ever talking to a reporter (perhaps that’s how they found me).
It’s been a few years, but I recall that the reporter went over the terms of what off the record meant and how he would use what I told him. I also showed him some hard copies of emails to read in my presence but took them back.